Just an (Eye) Drop of Poison

Earlier this month, California police arrested a man for spiking his girlfriend’s drink with poison following a quarrel. He didn’t deny it: the evidence included texts he’d sent to his buddies, bragging about his plan to make her pay for what she’d said to him.

But what poison did he admit to using? Dismiss any thoughts of the classic toxic elements such as arsenic, or murder mystery favorites such as cyanide. In this case, we’re simply talking about a bottle of Visine eye drops.

Surprised? You shouldn’t be. Eye-drop poisoning is more routine you might think. Remember the Ohio man arrested last year for sending his father to the hospital by putting two bottles of Visine into his milk? The Pennsylvania woman who’d been sneaking Visine into her boyfriend’s drinking water for three years? (The poor man suffered all that time with nausea, breathing and blood pressure problems). Oh, and let’s not forget the Wyoming teenager who was angry with her step-mother; the girl just pleaded no contest to aggravated assault charges this Friday.

Risky encounters with eyedrops have turned up on poison center roundups; the myth-busting website Snopes.com has tallied up even more. And those are lists of deliberate eye drop attacks. Let’s not forget the hazards posed by accidental poisonings; the U.S. Food and Drug Administration has issued a warning to parents about leaving eye drops containers around where they might be found by children.

Snopes took up the question to debunk an apparent belief that sneaking eye drops into a drink would basically induce a hilarious case of diarrhea — a scenario portrayed in a prank scene in the 2005 movie Wedding Crashers. Did I mention that Snopes specializes in myth busting? The website labeled the diarrhea scenario false and more. It went on to issue this warning: “Ingestion of such a concoction is downright dangerous making this ‘harmless’ form of retaliation fraught with hazard.”

Fraught with hazard? How, you may ask, does a formula that we trust enough to routinely drip it into our eyes suddenly sound so dangerous? There’s a reason, actually, why this is an eyes-only formula, why the Visine labels state: “If swallowed get medical help or contact a poison control center right away.” (As an aside, almost all the news stories mention Visine specifically because it’s most often used due probably to popularity. But let’s not forget there are others, including Murine Tears Plus, Eyesine and Tyzine).

Anyway, the active ingredient in these products is a compound called tetrahydrozoline, which turns to be a neat little arrangement of carbon, hydrogen, plus a little nitrogen. Or to be more specific it has the chemical formula: C13H16N2. It belongs to a family of compounds known for their ability to induce chemical reactions that either relax or constrict blood vessels. The former tend to end up in medications used to reduce blood pressure. The latter, which includes tetrahydrozoline, often go into nasal sprays or in eye drop formulas that are designed to “get the red out.”

This is not, by the way, a simple blood vessel squeeze. It derives from the way these compounds bind to receptors in the sympathetic nervous system, altering signals to the vascular system, triggering the change. It’s this action on the nervous system which puts tetrahydrozoline in the “neurotoxic” category on the Material Safety Data Sheet required of all manufactured chemical compounds.

And this neurotoxicity tells us why eyedrops are indeed fraught with hazard if you swallow them — or if you sneakily induce others to swallow them. Used as directed, they may indeed give you that clear-eyed look but that’s mostly due to the constriction of blood vessels in the eye. Internally they also induce vasoconstriction (as Toxnet calls it). The resulting symptoms are nothing, nothing at all like the Hollywood version of events. They include rapid heart beat, nausea, blurred vision, drowsiness, convulsions. The Toxnet entry, based partly on cases of children who swallowed a bottle of eyedrops or nosedrops left carelessly on a table or counter, notes that “drowsiness and mild coma” often alternate with periods of thrashing and hyperactivity.

What does this tell us, aside from the obvious home precautionary warnings (don’t leave your eye drop bottles lying around the house and, by the way don’t drink them)?

The record tells us that tetrahydrozoline while poisonous is not a top-of-line-lethal substance. According to the safety sheet, acute oral toxicity in lab mice stands at an LD50 of 345 mg/kg. (LD50 stands for lethal dose 50 percent, meaning the amount of a toxic substance that will kill half of a test population). For comparison, the LD50 of potassium cyanide in mice is 5 mg/kg. And that difference means that while people do end up the hospital, they tend to survive the stay. This is good news for victims and also for perpetrators, as so many of them end up arrested thanks in part to the very characteristic symptoms of eye drop poisoning.

Still as I also said earlier this is not really a tale of a classic homicidal poison like cyanide or one of devious plotting. This is more a tale of impulse, of anger, of grabbing a handy bottle. And, the California case I cited at the top of this story also reminds us that some people take movies like Wedding Crashers way too seriously; those incriminating texts of his indicated that idea was to make the girlfriend “crap for talking crap,” basically a scenario right out of the movie.

We could make a case here that entertainment comedies aren’t really the most reliable source of toxicology information. But for poisoners of the Visine caliber, here’s another recommendation as well — go for more serious entertainment. Perhaps all this trouble could have been avoided if the angry boyfriend watched CSI instead. In an episode titled “Revenge Served Cold” an eye-drop-spiked drink doesn’t just send the victim to the hospital, it kills him.